Eco-friendly preparation of durable superhydrophobic porous film for daytime radiative cooling

Daytime radiative cooling is a burgeoning cooling technology that reflects solar irradiation and radiates heat to outer space (3 K) to cool down terrestrial objects without using external energy. However, previously reported radiative cooling materials require complex technology, expensive equipment, or harmful chemicals, most of which are easily contaminated during outdoor applications. In this work, we proposed a simple and eco-friendly method with water as template to fabricate robust superhydrophobic porous polydimethylsiloxane (PDMS) radiative cooling film. The film possesses strong reflectivity and emissivity which results in outstanding cooling performance with ambient temperature drop of 11.52 °C, and has a superhydrophobic property with water contact angle of 165.7° and a sliding angle of 2.1° which results in excellent self-cleaning function. In addition, the prepared film shows low thermal conductivity of 0.1063 W m−1 K−1 which efficiently suppresses the heat exchange because of the air-filled voids within the film. Combining the self-cleaning property to prevent the surface from outdoor contamination or wetting, the film is promising to be widely used for long-term cooling for outdoor applications.Graphical abstract A superhydrophobic porous polydimethylsiloxane (S-P-PDMS) daytime radiative cooling film with high reflectivity and emissivity was prepared by a simple and eco-friendly template method, which achieved a cooling effect with sub-ambient temperature drop of 11.52 °C.